As I understand it, Sharepoint set's up scheduled tasks in your control
panel to manage these.

That was new for me
but i want also to know which file in the portal that manage this
process.

Not all together familiar with this area so had to refer back to my
Sharepoint book published by Digital Press (Laahs, McKenna, Vickers) which
is mighty useful & confirms that subscriptions  are stored  in the
system/Subscriptions folder within each workspace. Within this is a
subfolder called "templates" which contains the xsl style sheets used to
generate the text of the subscription  notifications.